Mass spectrometry (MS) is a major discovery tool in the life sciences. MS analyzes the molecular composition of a sample by ionizing the sample or the analyte molecules contained in the sample and then measuring the mass-to-charge ratios of the resulting ions. The mass spectra obtained by MS can be used to identify, characterize, and/or quantify the analytes of interest. In particular, variants of liquid chromatography-mass spectrometry (LC-MS) have been used for quantification of biomarkers and biologically active compounds, due to the high selectivity, sensitivity, speed, and simplicity of LC-MS.
However, MS has weaknesses and limitations. For example, matrix effects and isobaric interferences can present challenges to MS analysis, especially in complex samples.
Complex samples can include complex matrices that can interfere with a target analyte signal. Matrix effects can alter the signal response (e.g., by affecting the ionization efficiency of target analytes during MS), potentially leading to erroneous results and thus resulting in poor analytical accuracy, linearity, and reproducibility. Matrix effects can also obscure the signal at a particular mass transition of interest, rendering MS incapable of studying certain analytes in certain samples.
Internal standards are often added to samples in an attempt to address matrix effects. For example, internal standards can include isotopically (e.g., deuterium) labeled analogs of the target analyte, which can be used to correct for signal deviation because they are present in known amounts and possess similar chemical properties to the non-labeled analyte. However, deuterated internal standards, despite their common use, can be subject to deuterium scattering, which is generally considered to increase unpredictability and raise questions about the validity of experimental data.
In addition to matrix effects and the challenges posed by deuterium scattering, isobaric interferences can interfere with MS analysis. Such interferences can result, for example, from the presence of ions of identical mass to the analyte of interest. Because samples (e.g., biological or clinical samples) often contain a complex array of matrix components, isobaric interferences can complicate or hinder measurement of the internal standard, thereby preventing the signal deviation caused by matrix effects from being rectified.